FNR-246-W Purdue University Forestry and Natural Resources Size Does Matter–Nest Boxes for Wildlife Brian J. MacGowan, and Brian K. Miller, Extension Wildlife Specialists Department of Forestry and Natural Resources Purdue University, West Lafayette, IN 47907
Many people enjoy viewing wildlife on their nesting structures most beneficial for the wildlife property. The first step in attracting wildlife to species you wish to attract in your backyard. your backyard is to provide the specific habitat elements of food, water, cover, and space that your desired wildlife species require. Suitable cover is often one of the most limited habitat elements in backyard habitats. Over 50 wildlife species in the Midwest use cavities in live trees (den trees) or dead, standing trees (called snags) for nesting and denning cover. Unfortunately, yard management practiced by many of us does not encourage either of these critical habitat features needed by cavity nesting wildlife. New developments often lack an abundance of trees. Even when planted, many of the tree species selected for landscaping such as Bradford pear, flowering crabapple, or ash, do not favor development of natural cavities. Native hardwoods such as oak, sycamore, and beech trees readily form natural cavities, but may take many years to do so. While nest boxes are not a replacement for these species or wildlife habitat management, they are Live den tree. a great way to supplement natural cavities, make your backyard more attractive to cavity nesting Size and Location Matters species, and complement your landscape design Each wildlife species has specific at the same time. requirements for the dimensions and location Whether you purchase nest boxes or build of a nest cavity. Some of these requirements them yourself, a properly maintained nest box overlap among species. Bookstores and the can last for years. You can maximize their value Internet contain a myriad of nesting box plans by installing them at the proper heights and in and designs for most cavity-nesting wildlife the proper locations. They should be located species. While the outward appearance may near food, water, and other cover needed by your vary widely for these structures, the basic desired species. There are a few basic “rules function of a nest box is to attract a backyard of thumb” that will help you select and install resident.
Purdue University Cooperative Extension Service • West Lafayette, Indiana 1 FNR-246-W
The size of the entrance hole is a major Be aware of typical nest cavity dimension factor in determining what species can use the and placement characteristics for your target box and what species can be excluded from species. If you purchase or build a nest box, the box. This has been well documented in the make sure the dimensions and entrance hole Eastern bluebird. Now bluebird specialists are are the right size for the species you wish to promoting a box design with a long, narrow slit attract. Recommendations for some common at top rather than a round opening. These are Indiana backyard wildlife species are listed in preferred by bluebirds, but are unattractive to the following table. See the References Section house sparrows. for specific designs and detailed information The size of the internal cavity is arguably resources. more important than the entrance hole diameter.
Entrance Floor Total Height Average Hole height hole dimensions height of above start of Species Above Floor Location tips diameter inside box box ground nesting (in) (in) (in) (in) (ft) season Birds Place in orchards, pastures, or relatively open areas near grassy habitats (hunting areas). American 8 x 8 to mid-March 3 10-12 14-16 10-30 Facing south or west kestrel 9 x 9 to April and space at least ½ mile apart. Place 2-3” of wood chips in bottom of box. Face north or east, 1½ or 1 March to spaced 100 yards apart Bluebird 1 /8 vertical 6-7 4 x 4 11-12 3-6 early-April in open fields, orchards, slit and meadows. In hardwood forests, woodlots, or yards with late-April mature trees; need 40- 1 4 x 4 to Chickadees 1 /8 6-7 9-12 5-15 to early- 60% sunlight on box; 5 x 5 May one box per 10 acres. Place 1” of sawdust on nest box floor. Locate under an eave of House 1 4 x 4 to late-April 1 /8 6-7 9-12 5-10 a building or in a tree. wren 5 x 5 to May Can be free hanging. In mature hardwood Carolina 4 x 4 to mid-March 1½ 6-7 9-12 5-10 forests, forest edges, wren 5 x 5 to April yards with mature trees. In open fields near water, marshes, meadows, wooded
Tree 3 4 x 4 to late-April swamps; on a post in 1 /8 6-7 9-12 4 swallow 5 x 5 to May open areas near tree or fence, 30-100 feet apart; face entrance hole eastward.
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Entrance Floor Total Height Average Hole height hole dimensions height of above start of Species Above Floor Location tips diameter inside box box ground nesting (in) (in) (in) (in) (ft) season >20 for In forested wetlands or trees near marshes, swamps, >3 feet late-April and ponds; place in 4 wide x Wood duck 18 7 x 8 24-26 above high to early- deciduous trees, 30-100 3 tall water mark May feet from the nearest for posts in water; place 4” of wood water shavings in box bottom. In open areas at least
Purple 1 late-April 40ft from trees near 2 /8 1 6 x 6 6 8-20 martin to May utility wires and open water; paint white. Edge of mature late-March hardwood forest; to April Screech 6 x 6 to wooded parks or stream 2½ - 4 10-12 15-18 10-30 (will owl 8 x 8 edges. Place 2-3” of use year wood chips in box round) bottom. Shallow In moderate shade in the Mourning cones February - 12 - 6-16 crotch of a horizontal dove or nest to March tree limb. baskets In sheltered sites under American 7 x 7 to late-April On shelves - - 6-10 eaves or soffits, or on robin 8 x 8 to May tree trunks. Mammals Attach to tree trunk, side 1 of building, post. Face Bats (between - Variable Variable 12-15 Early April east on sites protected dividers) from the wind. In heavily wooded sites. Southern 4 x 4 to Locate hole on side flying 1¼ 6 9-12 10-30 5 x 5 of house close to tree squirrel trunk. February Locate in woodlots, 3 to March backyards with mature (located on Gray and 8 x 8 to (will trees in trees > 10” the side, 10-12 14-16 >15 fox squirrel 9 x 9 use year diameter. Face east or 2½” from round) south and fill half full of tree) dry leaves. Locate in coniferous Red (pine) 6 x 6 to 2½ - 4 10-12 15-18 10-30 woods or yards with squirrel 8 x 8 conifer trees. Data for table adapted from Mumford and Keller (1984), Henderson (1992), and Cornell Lab of Ornithology (http://birds.cornell.edu).
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Once basic cavity dimensions are met, and English house sparrows, non-native you need to choose a location based on the invasive species, to harass native cavity- requirements of your target species. Review nesters and take over a nest box. recommended locations in the table above and • Near the top of each side, leave gaps or the resources at the end of the publication. Ask drill 5/8 inch holes (at least 2 per side) yourself these questions. • Erect your nest box well before the average • Is it at the height the animal feels start of the nesting season. Some species comfortable? will set up their nesting territory 3 to 4 • Is the cavity protected from predators? weeks prior to egg laying. • Does the nest structure get the proper amount of sun or shade to provide Maintenance comfortable temperatures? After the nesting season, clean out the old nesting materials. While there are some • Is the nest structure near required food, species that like to build a new nest on top of water, and escape cover? old nests, most experts agree that cleaning out Choosing and placing nest structures that boxes is the best practice. This will minimize favorably meet these criteria will increase their parasite infestations and will make the box less use. Arrangement can also be important. Purple attractive for deer mice which can exclude birds martins need their boxes clustered into groups. the following spring. If unexpected residents Apartment houses or groups of gourd nests occupy a nest box, you may need to erect work well for purple martins. additional houses. Nest boxes for year round residents, such as screech owls, gray squirrel, Basic Design Tips and fox squirrel may be used throughout the Follow these basic design tips, maintenance winter. suggestions, and predator reduction advice to make your nest structures more useful to your backyard visitors. • Use quality materials that are weather resistant. Exterior grade plywood and lumber are good choices. Cedar and other rot-resistant woods are best. Avoid using treated lumber and metal. • Avoid painting or staining inside nest boxes. Painting the outside can prolong its life and may be attractive for some species (white for purple martins, for example). • The roof should be sloped to allow water runoff and should hang over the sides. • Drill at least four 3/8-inch drainage holes on the floor. • The roof or one side should open to allow easy access for cleaning. • Avoid perches. Natural cavities don’t have them and neither should your nest box. Bluebird box. Perches also allow European starlings
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Problem Species from ascending trees or poles. When mounting Monitor your nest boxes for use by house inverted cones or other predator guards, sparrows and European starlings. Competition locate them high enough on the pole or tree so by these species has been a leading factor in the predators can’t jump over them. decline of eastern bluebirds. Proper entrance When placing a predator guard on a tree or hole diameter will exclude starlings (1.5 inches pole, look around. If a predator can gain access or less) and house sparrows (1.25 inches or to the nest box from adjacent trees or buildings, less) from nest boxes. If you find a starling you will have to prevent access to all of them or house sparrow in your nest box, remove or select an appropriate location that is easier to the nest and all of its contents so the house is prevent predator access. available for your target species. However, this is just a temporary solution since they will Last, But Not Least simply rebuild their nest, although persistence One of the best reasons to put up a nest box is may produce results. House sparrows have for you. Place it in an area that is easily viewed abandoned a site after repeated (3-4 times) from an area you spend some quiet time like a destruction of their nests. You may also close reading area, the chair you sit in when enjoying the box entrance until the expected arrival time your morning cup of coffee, or a screened porch of your target species, although this would or deck. Then, sit back and enjoy the show! not work for year-round residents. Trapping and humanely dispatching starlings and house Acknowledgements sparrows is another method of reducing nest box The authors would like to thank J. B. competition. Dunning, Jr. and J. Castrale for providing many WARNING! House sparrows and European helpful comments that contributed greatly to this starlings are exotic species to North America. publication. They are not protected by law and can be legally trapped or killed using safe and approved methods. Most other species are protected by federal and state laws so be sure you properly identify your visitor before taking action. Boxes for some species may be utilized by native species other than your target species. For more information on laws and regulations protecting Indiana wildlife, see Animal Damage Management – Rules and Regulations in Indiana listed in the reference section. Predation by raccoons and house cats are serious problems in most areas of Indiana. Many nest box designs have predator guards that prevent nest predators from enlarging the entrance hole or from reaching into the box. For additional protection, install structures that prevent predators from climbing to the nest box. Generally, nest boxes on trees are easier Tree squirrel. targets than those mounted on poles. Using a cone or metal band can inhibit cats and raccoons
5 References Barquest, G, S. Craven, and R. Ellarson. Shelves, Houses and Feeders for Birds and Mammals, North Central Regional Extension Publication, No.338
5/04
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